When a watch case includes a caseband integrally formed with the back cover during manufacture, the fitting of the movement can only take place through the top of the caseband, after which the crystal is put into place in a sealed manner, for example by means of a packing interposed between the edge of the crystal and the interior edge of the caseband or the bezel. This manner of proceeding is generally reserved for mineral glass or sapphire crystals. If it is necessary to repair the movement, there are no means other than those of extracting the crystal from its seat, after which the movement may be removed from the case.
If the crystal projects from the caseband, it would be possible to employ a tool exhibiting a multitude of jaws capable of rocking through the action of levers, as is described for example in the patent document U.S. Pat. No. 3,074,156. It is certain however that such tool damages the periphery of the crystal and leaves scratches thereon, requiring recourse to a new crystal. The tool mentioned hereinabove is specific to removal of synthetic crystals.
In the case where the upper face of the crystal is at the same level as the caseband, which is the case with mineral glass and sapphire crystals or in the case in which the use of pliers is undesirable, one then has recourse to an extraction method for the crystal by driving it out under pressure as is described for example in the patent document CH-A-376 437. This method requires that the pressure prevailing within the case is increased until the crystal comes out of its housing. In order to proceed, the first portion of the broken type winding stem with which the movement is generally equipped is extracted and recess to the inlet thus created, an output duct for a pump is connected which permits increasing the pressure in the interior of the case up to the point where the crystal is driven out of its housing. Such a pump is described in patent document CH-A-541 181. However, since pressure on the order of 3 to 4 bars is necessary in order to extract the crystal, it will be understood that at the moment when such crystal is expelled from its seat, there occurs a violent displacement of air within the case, even if care has been taken to proportion the pump capacity to the volume of the case to be opened. According to the design of the watch, such air displacement may cause damage to certain interior elements of the watch. There has been seen for example dials and hands buckled, balance springs put out of adjustment, calendar discs bent or even bearings emptied of their oil.